Connecting computer to landline to make calls

Ok guys please help me out with this,
i wanna know how to connect my computer to a landline phone to make calls. let me explain it clearly :

i have a phone at my office which has free calling anywhere in india, so i want to connect my computer which is at home to my office phone to make calls through my computer for free.

i hope you get this.

one of my friend is living in india and his bro is living in kuwait, his bro gave my friend a software through which he connected his computer to his bro's phone in kuwait and now he is able to make calls anywhere in kuwait from his computer in india.
that makes it a free international calling.

does any1 got any idea how to do this stuff.
lemme know please would be very helpful.

Welcome to Voipuser forums.

Before you can be given advice on what you are asking you need to give more information about the type of connection being used by your office phone. Is it connected by voip or PSTN? If you want to connect you computer to PSTN you will need an FXO port. The other thing to consider is whether or not what you are trying to do is legal in your country.

I dont think so that its illegal, bcoz i have taken permission from my seniors to do that. anyways i m just using my own desk phone to do that.
and other thing is it is a PSTN connection.
anyways can i get any cheap VOIP service provider for cheap in india or kuwait with a monthly unlimited plan.?

Some countries do not allow or strongly regulate voip. You have not said in which county you reside. You have not said how your office phone is connected to the outside world - is it PSTN or intenet/voip? Is the phone on a network at your workplace?